1. Field of the Invention
The present invention pertains to a hydrojet with a drive unit and novel twin propellers, driven by the drive unit.
2. Prior Art
Such drives are known with a design wherein the drive unit proper, for example a diesel engine, is arranged within the hull and a transmission, being another part of the drive unit, is located in a gondola under the hull, from which shafts are led out at mutually opposite ends, the shafts being connected to the transmission and, at their outer ends, to one of two propellers shown as identical propellers, rotating in unison with them. Such a solution is described in DE 44 40 738 A1, in which an essential feature is a control device, which is arranged between the two propellers and eliminates the twist in the water after it leaves the propeller that is the front propeller in the direction of travel, so that this water flows to the propeller that is the rear propeller in the direction of travel with a higher energy, but likewise without twist, as it does to the front propeller. The control device is formed by guide blades and a shaft, which connects the gondola or the underwater housing to the hull. Such a drive is also described with some additional information in THE MOTORSHIP, Oct. 1996, pp. 47, 48: “Double the props: half the problem.”
The art further recognizes that although the propellers are of equal diameter, the geometry required for the rear propeller is different for the geometry required for the first propeller because of the water flowing to the propellers regarding pressure, flow rate, and other parameters. These geometrical requirements are well known to marine engineers and naval architects, persons skilled in the art. To design the front propeller and the different rear propeller for a particular application is readily accomplished according to known principles of marine engineering and naval architecture, and poses no problem or difficulty to those of skill in the art. Notwithstanding the foregoing, for watercraft of this type with two propellers, coaxially driven in the same sense, cavitation and other deleterious effects may occur.